J. Electrochem. Sci. Technol., 2020, 11(1), 68-83 - 68 - Modified Glassy Carbon Electrode with Polypyrrole Nanocomposite for the Simultaneous Determination of Ascorbic acid, Dopamine, Uric acid, and Folic Acid Khadijeh Ghanbari* and Sepideh Bonyadi Department of Chemistry, Faculty of physics and chemistry, School of Science, Alzahra University, Vanak, Tehran 1993891167, Iran ABSTRACT A fast and simple method for synthesis of Cu O-ZnO/PPy/RGO nanocomposite by electrochemical manner have been reported in this paper. For testing the utility of this nanocomposite we modified a GCE with the nanocomposite to yield a sensor for simultaneous determination of four analytes namely ascorbic acid (AA), dopamine (DA), uric acid (UA), and folic acid (FA). Cyclic voltammetry (CV) and Differential pulse voltammetry (DPV) selected for the study. The modified electrode cause to enhance electron transfer rate so overcome to overlapping their peaks and consequently having the ability to the simultaneous determination of AA, DA, UA, and FA. To synthesis confirmation of the nanocomposite, Field emis- sion scanning electron microscopy (FE-SEM), Raman spectroscopy, and electrochemical impedance spectroscopy (EIS) were applied. The linearity ranges were 0.07-485 μM, 0.05-430 μM, 0.02-250 μM and 0.022-180 μM for AA, DA, UA, and FA respectively and the detection limits were 22 nM, 10 nM, 5 nM and 6 nM for AA, DA, UA, and FA respectively Also, the obtained electrode can be used for the determination of the AA, DA, UA, and FA in human blood, and human urine real samples. Keywords : Electrochemical Sensor, Reduced Graphene Oxide, Ascorbic Acid, Dopamine, Uric Acid, Folic Acid Received : 31 July 2019, Accepted : 9 September 2019 1. Introduction One of the essential vitamins in the human diet is ascorbic acid (AA) and that is present in the mamma- lian brain along with various neurotransmitter amines [1]. Its utilization is in drinks and foods as an antioxi- dant to prevent and treatment of mental illness, com- mon cold, infertility, cancer, and AIDS [2]. Dopamine (DA) is a prominent neurotransmitter, which its responsibility is in the function of the cen- tral nervous, renal, hormonal and cardiovascular sys- tem [3-5]. Several serious neurological diseases such as Parkinson’s and schizophrenia are due to DA defi- ciency in the human body [6]. Another analyte that is the primary final purine metabolism product in the human body is Uric acid (UA). The abnormal amount of UA causes some of the diseases, such as Lesch-Nyhan syndrome and hyperuricemia, and gout [7]. A water-soluble vitamin folic acid (FA, N-[p- {[(2-amino-4- hydroxy-6-pteridinyl) methyl] amino} benzoyl]-l-glutamic acid, Vitamin M) is synthesized in nature by plants (green leaves, algae) and microor- ganisms (yeast, bacteria). FA determination in the food, pharmaceutical, and clinical samples has received much attention because newborns neural tube defects and diseases like megaloblastic anemia, cancer, Alzheimer’s are due to fail of that. FA partici- pates in the synthesis of nucleotide, cell division, gene expression, and gene expression with vitamin B12 [8,9]. The AA, DA, UA, and FA levels have intercommunication with the human physiological function. Deficiency or maladjustment in their levels may lead to many diseases. Therefore, simultaneous determination of AA, DA, UA, and FA has great importance in diagnoses, and controlling mentioned diseases. Research Article *E-mail address: kh.ghanbari@alzahra.ac.ir (kh_ghanb@yahoo.com) DOI: https://doi.org/10.33961/jecst.2019.00472 This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.